The invention relates to a phase regulating circuit employing a comparator, a pulse generator and a frequency divider in conjunction with a displacement pick-up, which constantly synchronizes the phase regulating circuit.
A displacement pick-up for the production of electric timing signals, at times at which predetermined points of a path which is to be traversed are exceeded, is known from U.S. Pat. No. 4,019,186, in which a light-transmitting rod is arranged along the path to be traversed, the rod having marks at predetermined points along the path to be traversed. As the light beam moves along the light transmitting rod, it is so influenced by the respective marks that it falls upon a photo element whose output signals represent the timing signals.
If a displacement pick-up of this type is utilized, for example, with a non-mechanical printer employing a laser beam for recording upon the surface of a recording drum, a part of the actual main recording beam, with the aid of the displacement pick-up, produces the timing pulses required for effecting the recordation of a row.
As a result of the geometric dimensioning of the displacement pick-up, the timing pulses can be produced only at specified intervals and the pulse train frequency obtained therefrom, between the individual single points determined by the marks on the light transmissive rod, must be multiplied and regulated. This type of pulse train production may be effected, for example, by utilization of a phase regulating circuit such as described in U.S. Pat. No. 3,705,361.
When a phase regulating circuit of this type is employed in association with the previously described displacement pick-up, gaps are formed in the produced pulse sequences as, during the recording operation, the scanning beam which functions to scan the displacement pick-up, returns from the end of one recording operation to the beginning of the next. A pulse gap of this type can, for example, comprise 20 percent of the time of the total horizontal cycle of the scanning beam. Consequently it is necessary to suitably compensate for the breakdown of the pulse train frequency during such gap.